Electronic monitoring devices are used by many government and private entities to detect and monitor the location of individuals wearing or associated with an electronic monitoring device. Electronic monitoring devices provide a cost effective solution to overcrowding of jails or prisons, and are often used to allow non-violent offenders to transition to society during a parole period, after being incarcerated for a period of time. Such devices can ensure confinement of the offender or monitored person to a particular location, such as at the offender's place of residence or at a rehabilitating institution, and may also determine whether the individual enters any places he is not allowed, also referred to as exclusion zones.
Electronic monitoring devices typically use either radio frequency (RF) communication with a second device, or Global Positioning System (GPS) technology to confirm the location of a monitored person, either in an absolute sense as with GPS, or relative to the second device which the electronic monitoring device is in RF communication with. For the purpose of knowing where the monitored person is, electronic monitoring devices are often designed to be attached to a monitored person for monitoring the movements or other activities of the person. Such electronic monitoring devices often include a tamper sensor for sensing tampering with the device or removal of the device from the person to whom the device was attached. The electronic monitoring device may then produce a tamper signal which is transmitted to an external receiver.
A variety of methods are used to detect whether a monitoring device has been removed from a monitored offender's limb. For example, U.S. Pat. No. 5,471,197 to McCurdy et al. describes a personnel monitoring apparatus, including a strap with an optical fiber in the strap for optically coupling to an optical emitter and detector in the monitoring device. A comparator compares the optical signal and a reference signal.
Even in light of these methods of detecting tamper, advancements in this area would be welcomed.